As another outside ad dropped in North Carolina’s U.S. Senate race, one national report called the state “ground zero” in the TV war of the 2014 election.

A liberal political action committee called Patriot Majority USA launched an ad aimed at House Speaker Thom Tillis, the perceived front-runner in the Republican primary. The group is spending $500,000 to run the 30-second ad.

It’s the second outside ad on behalf of incumbent Democratic Sen. Kay Hagan. The Senate Majority PAC, aligned with Senate Majority Leader Harry Reid of Nevada, spent over $1 million in December.

Both pale in comparison to the money spent by Americans for Prosperity. The conservative group has spent at least $6.5 million – by some counts more than $8 million – on ads attacking Hagan and her support of the Affordable Care Act.

Politico said Wednesday that figure puts AFP on pace to spend $27 million in the state, making it “ground zero” of the mid-term elections.

Like the earlier Senate ad, the Patriot Majority spot focuses on Tillis, one of several GOP candidates. It accuses him of siding with health insurance companies and special interest groups.

“These new attack ads showcase another example of Hagan’s hypocrisy,” Tillis said in an email to supporters. “While Kay Hagan denounces the use of outside funds against her, her liberal cronies in DC are dumping another half a million dollars in attack ads to falsely attack me. Kay Hagan and DC liberals know that our message is resonating. …”

Hagan has criticized the conservative group and its sponsors, Charles and David Koch, for running such ads and pushing what she calls a special-interest agenda.

“Koch Brothers on track to spend $27 million in NC b/c they want to control the person in this Senate seat,” she tweeted Wednesday.

According to the Center for Responsive Politics, donors to the Patriot Majority PAC include the Democratic Legislative Campaign Committee and the public employees union, AFSCME. But like Americans for Prosperity, the liberal committee generally doesn’t disclose its donors.

Tillis and other Republicans were quick to call out Hagan for denouncing AFP attacks but not attacks by liberal groups.

Hagan spokeswoman Sadie Weiner said Hagan has “no control over outside groups.”

Hagan has criticized not only the AFP ads but what she calls the Koch brothers’ conservative agenda. The brothers, oil company billionaires, bankroll a variety of conservative groups.

Hagan supports the Democratic-sponsored DISCLOSE act that would require more transparency from political groups.